This present disclosure relates to toners and developers containing the toners for use in forming and developing images, and in particular to polyester emulsion/aggregation toners formed using polyions as coagulants. The disclosure also relates to processes for producing and using such toners and developers.
Emulsion aggregation toners are excellent toners to use in forming print and/or xerographic images in that the toners can be made to have uniform sizes and in that the toners are environmentally friendly. U.S. patents describing emulsion aggregation toners include, for example, U.S. Pat. Nos. 5,370,963, 5,418,108, 5,290,654, 5,278,020, 5,308,734, 5,344,738, 5,403,693, 5,364,729, 5,346,797, 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256, 5,501,935, 5,723,253, 5,744,520, 5,763,133, 5,766,818, 5,747,215, 5,827,633, 5,853,944, 5,804,349, 5,840,462, and 5,869,215, the entire disclosures of which are incorporated herein by reference.
Two main types of emulsion aggregation toners are known. First is an emulsion aggregation process that forms acrylate based, e.g., styrene acrylate, toner particles. See, for example, U.S. Pat. No. 6,120,967, the entire disclosure of which is incorporated herein by reference, as one example of such a process. Second is an emulsion aggregation process that forms polyester, e.g., sodio sulfonated polyester, toner particles. See, for example, U.S. Pat. No. 5,916,725, the entire disclosure of which is incorporated herein by reference, as one example of such a process.
Emulsion aggregation techniques typically involve the formation of an emulsion latex of the resin particles, which particles have a small size of from, for example, about 5 to about 500 nanometers in diameter, by heating the resin, optionally with solvent if needed, in water, or by making a latex in water using an emulsion polymerization. A colorant dispersion, for example of a pigment dispersed in water, optionally also with additional resin, is separately formed. The colorant dispersion is added to the emulsion latex mixture, and an aggregating agent or complexing agent is then added to form aggregated toner particles. The aggregated toner particles are heated to enable coalescence/fusing, thereby achieving aggregated, fused toner particles.
Addition of a coagulant during the emulsion/aggregation process is an important step, to assist in aggregation of the primary polymer, colorant, and the like particles. For example, U.S. Pat. No. 6,120,967, mentioned above, describes a process where styrene acrylate-based resins are used to form toner particles, and in which a cationic coagulant such as poly-aluminum chloride, aluminum sulfate, zinc sulfate, alum, and dialkyl benzenealkyl ammonium chloride is used as the coagulant. However, different coagulants are used in polyester-based resin emulsion/aggregation processes. For example, U.S. Pat. No. 5,916,725, also mentioned above, describes a process where polyester-based resins are used to form toner particles, and in which the coagulant is a small organic amine, such as 2-methyl-1,5-pentanediamine.
In other polyester-based resin emulsion/aggregation processes, zinc acetate has been extensively used as a coagulant. See, for example, U.S. Pat. Nos. 6,500,597, 6,743,559, and 6,756,176, which disclose the use of metal salts, such as aluminum sulfate, aluminum chloride, zinc sulfate, magnesium sulfate, magnesium chloride, potassium-aluminum sulfate, or zinc acetate, as coagulants for producing polyester toners in emulsion/aggregation processes.
However, a problem exists with the use of such metal salts as zinc acetate in producing polyester toners. In particular, only a small proportion of the zinc acetate, about 2 to 3 weight %, gets incorporated into the toner particles. The remaining zinc acetate is in the aqueous phase, and must be filtered and separated before the aqueous phase can be discharged into the environment. This separation thus adds a significant cost to the toner production and waste disposal. The low rate of incorporation of zinc acetate into the toner particles is believed to be primarily due to its high solubility in water and the partial dissociation of the zinc acetate However, coagulants such as polyions have not previously been used in producing polyester toners, such as sulfonated polyester toners, because the sulfonate groups on the polyester resin particles are not sufficient to provide a controlled aggregation or coalescence in the presence of the more active polyion coagulants.
Accordingly, there is a need in the art for improved emulsion aggregation toner processes, particularly for use with polyester toner particles, that provide an efficient, controlled process without increasing the separation and disposal costs.